T-Mobile USA lost another 50,000 customers in Q2 2011 according to its quarterly earnings report issue today. It continues a long-running trend of T-Mobile failing to attract and keep customers, despite having the most affordable rates among the top four carriers in the U.S.

Losing 50,000 customers is actually an improvement for T-Mobile, which lost more than 93,000 subscribers during this same period last year. However, with weak sales and retention, it’s no wonder that Deutsche Telekom, T-Mobile USA’s parent company, is trying to dump the operation in a sale to AT&T.

We previously asked how users would save T-Mobile USA, but nothing seems to work. T-Mobile has added some top-level Android smartphones, expanded the foothold of its 4G HSPA+ network, offered more “unlimited” rate options, and had many sales designed to attract new customers. Despite these efforts, T-Mobile struggles to have a net gain of customers while AT&T, Sprint, and Verizon continue to add to its subscriber base.

There are now almost 10 million customers using a 3G/4G smartphone on T-Mobile. That’s a 50 percent increase from the number of people during Q2 2010. It’s worth noting that T-Mobile previously blamed a lack of 3G phones for its loss of customers, so maybe offering better options and covering more people actually did lead to improved performance. T-Mobile 4G HSPA+ theoretical speeds of up to 42 Mbps now reaches 170 million people in 100 markets.